Funded by Results Driven Agriculture Research (RDAR)
Introduction and Objective
In the Peace region, producers use several grasses and legumes in their forage establishments to provide feed to their livestock. Perennial grass–legume mixtures have been noted to increase yield and improve quality compared to grass monocrops. However, across Alberta, questions from producers focus on how to improve their pastures or hay lands using combinations of grass and legume species to optimize forage-livestock systems. In addition to the enormous benefits of perennial mixtures to the beef cattle sector, mixed perennial forages can also provide other beneficial ecosystem functions. The objective of this study was to examine a variety of grass–legume mixtures and compare them to grass monocrops in terms of their yielding abilities, qualities, impacts on soil health and water use efficiencies (WUE), and beef cattle performance using the CowBytes® ration-balancing program.
Methods
The field experiment was established on 26 June 2020 at the Fairview Research Farm in Fairview, Alberta. The field had a history of several years of wheat-canola rotation. The research was arranged in a randomized complete block design with four replications. The treatments comprised of six simple grass–legume (one grass and one legume) and 18 complex diverse perennial forage species (i.e., three or more grass-legume) mixtures, thus three only-grasses mixtures, two only-legume mixtures and 13 grass-legume mixtures. In addition, there were five pure stands of perennial grasses which were used for comparisons. The grass species used in mixtures and monocultures were wheat grass (kirk crested wheatgrass and greenleaf pubescent), orchard grass, timothy grass, meadow bromegrasses, and hybrid bromegrass (Table 1).
Seeding was done using the 6-row Fabro plot drill equipped with disc-type openers at 9″ on 2m wide x 8m long plots. Volumetric water content measurement was undertaken during the growing seasons of 2023 to aid in estimating the water-use efficiency of treatments. In addition, soil samples were collected from individual plots to evaluate soil nutrients, microbial activity, and carbon sequestration, as well as soil compaction at the end of the project. The soil samples were analyzed at the Chinook Applied Research Association (CARA) and Natural Resources Analytical Laboratory (NRAL).
In the first, second and third years of forage production (2021, 2022, and 2023), forage dry matter (DM) yield was determined and forage samples were analyzed for feed quality at A&L Laboratory, Ontario, Canada. The results for the first and second years of forage production (2021 and 2022) are available in the PCBFA annual reports (PCBFA, 2022, 2021).
esults
Forage DM yield and quality indicators of perennial forage for 2023.
Forage Yields were variably significant. The top 5 highest yields were recorded in M6 (4398 lb/ac), Mix 14 (4193 lb/ac), Mix 23 (3952 lb/ac), Mix 4 (3880 lb/ac), and Mix 21 (3791 lb/ac). Overall, monocrop grasses and “only-grasses” mixtures were poor in DM yield compared to grass-legume mixtures. The highest producing monocrop was Fleet meadow bromegrass (1677 lb/ac). This indicated that Mix 6 produced 2721 lb/ac more than Fleet meadow bromegrass whereas M21 produced 2114 lb/ac more. This is approximately two bales of 1000 lb more than having grass monocrops.
Crude Protein (CP): CP contents for all treatments were between 11.7 for Mix 0 and 18% for Mix 3 (Table 2). Grass–legume mixtures were generally superior to grass monocrops as observed in Mix 3 (18%), Mix 14 (17.8%), Mix 23 (17.5%), Mix 16 (17.5%), and Mix 6 (17.2%). The number of legumes present in a particular treatment did not significantly affect the amount of CP in forage. The CP contents in all forage treatments were adequate or even above adequate to meet the protein needs of cattle at different developmental stages (i.e., gestation, lactation, calving).
Neutral Detergent Fiber (NDF), Acid Detergent Fiber (ADF) and Neutral Detergent Fiber Digestibility (NDFD-48hr): NDF across all treatments ranged from 45.6% for Mix 3 to 60% for greenleaf pubescent wheatgrass, while ADF varied from 31.3% for kirk crested wheatgrass to 38.4% for M4. The treatments Mix 3 (45.6%), Mix 12 (46.6%), M16 (46.5%) and M17 (46.2%) were lower in NDF, whereas Mix 3 and kirk crested wheatgrass ranked best in ADF (33.7% and 31.3%, respectively) when compared to all the other forage treatments. This makes Mix 3, the treatment with the lowest NDF and ADF, hence the best performers in terms of crude fiber contents (Table 2). Furthermore, grass monocrops recorded the highest NDFD compared to grass-legume mixtures. The greenleaf pubescent wheatgrass (66.5%), Fleet meadow bromegrass (65.7%), and kirk crested wheatgrass (65.7%) had the highest NDFD. A higher NDFD will allow cows to eat more and digest efficiently to boost their performance.
Total Digestible Nutrients (TDN): Energy levels in all forage treatments were above 61%. The highest TDN was in grass monocrops and “only grasses” mixtures such as Fleet meadow bromegrass (68.1%), orchard grass (66.8%), Mix 0 (66.4%), and timothy grass (66.2%). Notably, grass-legume mixtures did not outperform grasses in energy levels, even though both recorded TDN values above 61% (Table 2). As a rule of thumb for energy requirements (55 – 60 - 65), the energy levels in forages are adequate to meet the requirements for dry and pregnant cows (54% and 55%, respectively), 59% for young cattle and 62% for lactating cattle.
Water Use Efficiencies (Biomass and Crude Protein): The top four performers for biomass WUE were Mix 6, Mix 14, Mix 21, and Mix 23. Among these treatments, Mix 6 (1707 lb inches-1) had the highest WUE (Table 3). Generally, grass-legume mixtures were better at using water efficiently to produce biomass compared to grass monocrops. Crude protein WUE was also variably significant. The top four performing treatments were Mix 6 (29124.1 lb CP inches-1), Mix 14 (26354.7 lb CP inches-1), Mix 5 (24870.1 lb CP inches-1), and Mix 4 (22441.2 lb CP inches-1) (Table 3).
Beef Cattle Performance on Forage Mixtures: The CowBytes® ration–balancing software used to predict the performance of a 7-month dry gestating beef cow showed that Mix 4, Mix 9, and orchard grass monoculture were superior in meeting the average daily gain (0.25 lbs/day) and energy requirements than other mixtures and monoculture grasses. Furthermore, using these forage mixtures was cost effective, reducing production costs by almost $65 per head per day. In addition, Mix 1, Mix 12, M17, and orchard grass were greater in supporting the average daily gains (1.8 lb/day) of a steer whereas M1, M13, M15, Timothy Grass and Orchard Grass supported lactating beef cows to obtain average daily gains of 0.25 lb/day.
Soil Health and Provision of Ecosystem Services: Soil compaction was improved in forage stands with high plant diversity. Substantial reduction in soil compaction was recorded in forage treatments of Mix 14, Mix 22, and Mix 23. A reduction in soil compaction enhances the movement of plant roots, which enables an effective utilization of nutrients and water in the soil. In addition, Mix 9 improved the soil infiltration rate (0.79 cm hr-1). Soil carbon dioxide production can be used as a proxy to estimate the increased soil microbial activity, which is important for soil health. This is because many microorganisms are vital for the breakdown of organic material, which releases nutrients into the soil. At the end of study, treatments of Mix 0, Mix 7, and Mix 21 (0.63-0.66 mg CO2 g–1 soil) had higher CO2 production than other mixtures and monoculture grasses. Soil carbon accumulation is vital for effective mineralization and improvement of the soil structure. At the end of the study, Fleet meadow bromegrass monoculture significantly had the highest rate of soil carbon sequestration, followed by Mix 0 (7122 lb C ac-1 yr-1).
Conclusion
The study has shown the yielding abilities and quality indicators of both grass-legume mixtures, grass monocrops and “only-grasses” mixtures. Overall, grass-legume mixtures had the highest DM yield and CP and lower NDF and ADF levels, while grass monocrops and grass-only mixtures were higher in NDFD-48hrs and TDN. Even though several grass-legume mixtures contained many species of legumes, this did not significantly influence the CP content. Furthermore, grass-legume mixtures were better at using water efficiently to produce biomass and crude protein compared to grass monocrops and “only-grasses” mixtures. Grass monocultures and grass-only mixtures provided sufficient energy levels to support steers, gestating and lactating beef cows in achieving their expected average daily gains. In general, grass-legume mixtures also improved soil compaction whereas grass monocultures and only-grass mixtures improved soil carbon sequestration.
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